Electroplating



Patented Feb. 23, 1943 ELECTROPLATIN G Richard 0. Hull, Lakewood, and Clayton F. Ruchensaal, Cleveland, Ohio, assignors to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application July 20, 1939, Serial No. 285,512

4 Claims.

This invention relates to the electrodeposition of nickel and is more particularly directed to nickel plating compositions, nickel plating baths, and to processes for the electrodeposition of nickel wherein a methyl naphthalene monosulionic acid or sulfonate and sulfite cellulose waste are used as addition agents.

It was early proposed in the Lutz-Westbrook Patent 1,818,229 to effect the electrodeposition of bright nickel in the presence of naphthalene sulfonates, the preferred addition agents including sulfonates well known as textile wetting agents. While baths containing such addition agents give good results, they are of rather low surface tension, they must be operated within a rather narrow current density range, and they produce deposits which though smooth and bright tend to be rather hard.

More recently other specific sulfonates have been suggested as in the Schlotter Patent 1,972,693. Deposits of good character are obtainable using such addition agents, but the deposits while bright tend to be pitted. Still other sulfonates have been suggested but these similarly are subject to various technical disadvantages and none of them offer any marked advance over the teachings of the Lutz-Westbrook patent.

Other textile wetting agents have been proposed for use in nickel plating as shown in the British Patent 472,514, and while the various wetting agents have some beneficial effects, they are nonetheless subject to certain disadvantages. One objection to the use of these wetting agents results from the marked lowering of the surface tension of the plating solution, the low surface tension of the solution causing oil which is introduced in various unavoidable ways to become emulsified and dispersed in the bath. This dispersed oil causes streaks and spots on the nickel deposits obtained from such baths. The impracticability of avoiding accidental and inadvertent introduction of oil into these low surface tension baths has made it necessary to adopt such extreme measures as continuously filtering the solution or treating it with activated carbon to remove the oil.

It is an object of this invention to provide compositions, baths, and processes by the use of which there may be obtained nickel deposits 1 which are brilliant, smooth, ductile, and free from pits. It is a still further object of this invention to provide compositions, baths, and plating processes by the use of which thick nickel deposits may be obtained which are smooth and bright in contrast to the similar deposits heretofore frequently obtained which while bright are not entirely smooth. It is a still further object of this invention to produce bright nickel baths of relatively high surface tension. It is a still economical to use.

further object to provide nickel plating compositions, baths and processes which are simple and Further objects of this invention will become apparent hereinafter.

The foregoingand other objects of this invention are accomplished by the use of a methyl naphthalene monosulfonic acid or sulfonate in combination with sulfite cellulose waste. Nickel plating baths containing this mixture of organic agents produce nickel deposits which are brilliant, smooth, ductile, and free from pits, and the deposits are smooth even at relatively great thicknesses. Baths containing these agents are of relatively high surface tension with the result that oil and similar foreign materials do not become dispersed in the bath if accidentally or inadvertently introduced thereinto.

The methyl naphthalene monosulfonic acid used will ordinarily be composed of a mixture of alphaand beta-methyl naphthalene sulfonic acids since the commercial methyl naphthalene sulfonated is such a mixture. We have separated the alphaand beta-sulfonic acids and have tried each separately as an addition agent for nickel plating according to the present, invention. The two forms seem equally effective so that it appears of no great importance whether one or a mixture is used. Since the mixture is available commercially, it will ordinarily be found most economical to use the mixture.

It is immaterial for the purposes of this invention whether a free methyl naphthalene sulfonic acid or one of its water-soluble salts is used as an addition agent for nickel plating baths. The actual compound contained in the bath will depend upon the pH and the term methyl naphthalene monosulfonic acid as used herein is meant to embrace the free acid as well as its water-soluble salts or derivatives. found that it is somewhat difiicult to separate the free acid or its sodium salt from solution in the process of manufacture, and it has been found expedient to convert the acid to the nickel salt to aid in its production in a pure condition. As a practical matter, it may frequently be. found desirable, therefore, to add the methyl naphthalene sulfonic acid in the form of its nickel salt.

We have found that the presence of unsulfonated methyl naphthalenes in a nickel plating bath causes the deposits to be brittle and pitted.

The unsulfonated methyl naphthalenes can be We have methyl naphthalene monosulfonate, amounts as high as perhaps one-tenth of one per cent can be tolerated and the amount should in no event greatly exceed about one per cent.

The amount of methyl naphthalene sulfonic acid used may widely vary but it is preferred to use from about .25 to grams per liter. More specifically, it has been found that the best results are obtained with-from about one to three grams per liter. It will be understood that methyl naphthalene nickel sulfonate and other soluble salts maybe used in similar amounts.

The effects of the methyl naphthalene sulfonic acid addition agents of this inventiorr are augmented and synergized by the use therewith of sulfite cellulose waste. Sulfite cellulose waste is a well-known commodity of commerce and it has previously been found useful in certain plating systems as an addition agent in its own right. Lignin sulfonic acids derived from sulflte cellulose waste may be used instead in the same amounts and with substantially the same results. This and other derivatives of similar character are known to be equivalent to sulfite cellulose waste and they require no extended discussion.

The amount of sulfite cellulose waste to use in conjunction with a methyl naphthalene monosuli'onic acid may vary -geldelmbut in general it will be found desirable to use from about .25 to grams (on a dry basis) per liter. More specifically, it wil1 be found preferable to use from about one to five grams per liter of sulflte cellulose waste.

The addition agents of this invention may advantageously be merchandised as a mixture containing the proper proportions of methyl naphthalene sulfonic acid and sulfite cellulose waste. The mixtures may be dry or may be offered as concentrated solutions. Suclrcompositions will ordinarily contain about equal amounts of methyl naphthalene sulfonic acid or a methyl naphthalene monosulfonate with sulfite cellulose waste. More broadly, to produce. plating baths Example A -nickel plating bath of this invention was made up with the following constituents:

Nickel sulfate (NiSO4'7H20) grams per liter 250 Nickel chloride (NiClz-BHzO) grams per liter 15 Boric acid (H3303) do 35 Sulfite cellulose waste do 2 Methyl naphthalene nickel monosulfonate grams per liter 1.5 Temperature "degrees centigrade 50 pH (electrometric) 5 Employing this bath at about the optimum current density of fifty amperes per square foot excellent nickel deposits 0.002 inch thick were obtained.

The bath of this example was found to operate best at a pH between about 4.8 and 5.2, determined electrometrically. The bath was found to operate best at temperatures from about 45 to 60 C. while the best results were obtained from about 50 to 55 C.

The bath of this example was found to have a wide bright current density range extending from about 5 to '75 amperes per square foot when the solution was not agitated. When the bath was agitated during plating, the bright current density range was still further extended.

While the best results have been obtained with the bath composition show, it will be understood that the addition agents of this invention may be used with any of the various baths known to the art for the electroplating of nickel. Particular reference is made in this connection to the various plating baths which have found commercial application for thedeposition of bright nickel prior to chromium plating.

While we have shown certain compositions, baths, and processes it will be understood that one skilled in the art may without departing from the spirit of this invention readily devise numerous practices employing methyl naphthalene monosulfonic acid and sulfite cellulose waste as addition agents for nickel plating.

We claim:

1. An acidic nickel plating bath including about 250 grams per liter of nickel sulfate, 15 grams per liter of nickel chloride, 35 grams per liter of boric acid, about 1 to 5 grams per liter of sulfite cellulose waste, and about 1 to 3 grams per liter of an addition agent selecter from the group consisting of methyl naphthalene monosulfonic acid andits salts.

2. A nickel plating bath including nickel sulfate, nickel chloride, boric acid, from about 0.25 to 15 grams per liter sulfite cellulose waste, and from about 0.25 to 5 grams p r liter of an addition agent selected from the group consisting of methyl naphthalene monosulfonic acid and its salts.

3. In a process for the electrodeposition of nickel, the step comprising effecting electrodeposition in the presence of nickel sulfate, nickel chloride, boric acid, about 0.25 to 15 grams per liter sulfite cellulose waste, and about 0.25 to 5 grams per liter of an addition agent selected from the group consisting of methyl naphthalene monosulfonic acid and its salts.

4. In a process for the electrodeposition of nickel, the step comprising effecting electrodeposition in the presence of about 250 grams per liter of nickel sulfate, 15 grams per liter of nickel chloride, 35 grams per liter of boric acid, about 1 to 5 grams per liter of sulfite cellulose waste, and about 1 to 3 ,grams per liter of an addition agent selected from the group consisting of methyl naphthalene monosulfonic acid and its salts.

RICHARD O. HULL. CLAYTON F. RUEBENSAAL. 

